EN
The physico-chemical and biological properties of 19 strains of parainfluenza-3 virus were studied. These had been isolated in the years 1970-1973 during periodic enzootics of the respiratory tract in cattle. The study demonstrated the existence of variants differing in infectious and haemagglutination properties, in immunogenic activity as well as in sensitivity to various temperatures, showing different intensities of growth in the cells of selected animal organs. Out of the 19 investigated field strains two strains were chosen for our special purpose. These were isolated from the lungs and nasal discharge of an affected calf and, as compared to the other investigated strains, showed antigenic properties which most properly met the requirements of specific prophylaxis.